The general procedure normally used to tune a trumpet consists of a variation of the length of the so-called "flue pipe". Such variation is achieved by means of extensible sections which enable a longer flue pipe.
Obviously, since the tonality of a trumpet depends on the length of the flue pipe, in order to achieve different notes of the musical scale it is necessary to enlarge or shorten the length of such flue pipe, thereby modifying the route of the air flow and providing the instrument the necessary distance to obtain a frequency which determines its proper general tuning.
Up to now, trumpet manufacturers based the tuning of the instrument on a part known as "tudel", formed by a series of extensible pipes known as "general pump", which can be lengthened to tune the trumpet. Such "tudel" is a part located before the so-called instrument "body". Therefore, the tuning section of trumpets is located before the so-called trumpet body.
When the musical instrument does not enable its tuning at the tudel, due to its length, the manufacturer has either to lengthen such tudel, as in the case of the Piccolo trumpet or to lengthen the bell itself, previously denominated flue pipe. Such lengthening is performed at the end of the body. This tuning procedure is normally applied to the so called B-Cb trumpet.
In summary, trumpets can be tuned either at the mouth side or "tudel" section, at the "general pump" section, which is the bend located before the body, before the tudel itself, or even at the bell section located after the instrument body. This section is formed by a single piece comprising the bell and the relevant output bending.
When the tuning is to be performed after the trumpet body, it is necessary to replace such bell, i.e., the section comprising the output bending and the relevant bell.
On the other hand, and as far as the structure of the instrument is concerned, in the case of trumpets and similar instruments, they are formed by different properly assembled metal parts. Sometimes, such parts are of a cylindrical shape, with or without curved sections, normally, semi-circumferential, although they can also present a trunco-conical shape with a curved generative, as it is the case of the bell.
In any case, a metal pipe or plate is used to obtain such pieces. They are conveniently shaped by means of a deformation either through a hot- or cold- process. These pieces are usually moulded, either manually, by means of hammers or any other adequate tool, or mechanically, by means of hydraulically- or mechanically operated shaping machines.
Obviously, and since most pieces are generated ones, the use of plates increases the complexity of the operation, especially when they have to be closed. Therefore, it is more appropriate--in principle--to use pipes. However, they also present--especially when manufacturing bells--the problem derived from the difference in diameters, and therefore, they usually different wall thicknesses, with an excessive thickness on the end with larger diameter and an insignificant thickness at the other end.
Another fact to be taken into consideration is that mouthpieces used by brass instruments are normally formed by a single piece split into three different parts, the "output cone", which is directly attached to the instrument, and more specifically, to the section known as tudel. Therefore, such output cone can have different inner dimensions, depending on the needs of the musician. The second part of the mouthpiece is the so-called "bowl", which determines a cavity to collect vibrations produced by the lips of the musician. Such bowl, depending on the characteristics of the musician and the type of music being played, will have a larger or smaller size, with different accepted shapes and deepness. The third part is formed by the so-called mouthpiece "ring" or "edge", which is the element coming into contact with the lips of the musician. This part is considered to be very critical, due to the preferences of the musician, as far as the shape of the rings is concerned.
The three elements forming the mouthpiece of a brass instrument are normally formed by a single piece, which, in some instances can have a detachable edge or ring. Therefore, neither the bowl nor the output cone can be varied and the musician will have to purchase a complete set each time he wishes to use a specific mouthpiece, without the possibility of replacing them by others more suitable to his specific needs or preferences.